Phosphorescent materials

ABSTRACT

Compounds comprising a ligand having a quinoline or isoquinoline moiety and a phenyl moiety, e.g., (iso)pq ligands. In particular, the ligand is further substituted with electron donating groups. The compounds may be used in organic light emitting devices, particularly devices with emission in the deep red part of the visible spectrum, to provide devices having improved properties.

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, The University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to organic light emitting devices (OLEDs).More specifically, the present invention related to phosphorescentmaterials comprising a ligand having a quinoline or isoquinoline moietyand a phenyl moiety, e.g., (iso)pq ligands, which is further substitutedwith electron donating groups. These materials may provide deviceshaving improved performance.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY OF THE INVENTION

Compounds are provided having the formula:

M is a metal having an atomic weight higher than 40. L is an ancillaryligand. m is the oxidation state of the metal M. Preferably, M is Ir. nis at least 1. A is a fused carbocyclic or fused heterocyclic ring. Eachof R_(a) and R_(b) may represent mono, di, tri, or tetra substituents.Each R_(a) substituent is independently selected from the groupconsisting of hydrogen, deuterium, alkyl, heteroalkyl, aryl orheteroaryl groups. Each R_(b) substituent is independently selected fromthe group consisting of hydrogen, deuterium, alkyl, heteroalkyl, aryl orheteroaryl groups. At least two R_(b) substituents are selected from thegroup consisting of alkoxy, aryloxy, alkyl amino, and aryl amino.

Preferably, L is a monoanionic bidentate ligand. More preferably, L is

and R_(x), R_(y), and R_(z) are each independently selected from thegroup consisting of hydrogen, deuterium, alkyl, heteroalkyl, aryl orheteroaryl groups. Most preferably, at least one of R_(x) and R_(y)contains a branched alkyl moiety with branching at a position furtherthan the α position to the carbonyl group. In one aspect, at least oneof R_(x) and R_(y) is isobutyl. In another aspect, R_(z) is hydrogen.

In one aspect, the compound has a formula selected from the groupconsisting of:

In another aspect, the (iso)pq ligand is selected from the groupconsisting of:

Specific compounds are also provided. In particular, the compound isselected from the group consisting of Compound 1-Compound 7.

In one aspect, the compound has an emissive spectrum having a peakwavelength of about 650 nm to about 700 nm.

A first device comprising an organic light emitting device is alsoprovided. The organic light emitting device further comprises an anode,a cathode, and an organic layer disposed between the anode and thecathode. The organic layer comprises a compound having the formula:

M is a metal having an atomic weight higher than 40. Preferably, M isIr. L is an ancillary ligand. m is the oxidation state of the metal M. nis at least 1. A is a fused carbocyclic or fused heterocyclic ring. Eachof R_(a) and R_(b) may represent mono, di, tri, or tetra substituents.Each R_(a) substituent is independently selected from the groupconsisting of hydrogen, deuterium, alkyl, heteroalkyl, aryl orheteroaryl groups. Each R_(b) substituent is independently selected fromthe group consisting of hydrogen, deuterium, alkyl, heteroalkyl, aryl orheteroaryl groups. At least two R_(b) substituents are selected from thegroup consisting of alkoxy, aryloxy, alkyl amino, and aryl amino.

Specific examples of devices comprising inventive compounds areprovided. In one aspect, the compound used in the first device isselected form the group consisting of Compound 1-Compound 7.

The various specific aspects discussed above for Formula I are alsoapplicable to a compound having Formula I when used in the first device.In particular, specific aspects of M, L, R_(a), R_(b), R_(x), R_(y),R_(z), and the (iso)pq ligand moiety of the compound having Formula Idiscussed above are also applicable to a compound having Formula I thatis used in the first device.

In one aspect, the organic layer is an emissive layer and the compoundhaving Formula I is an emitting dopant. In another aspect, the organiclayer further comprises a host. Preferably, the host is a metal8-hydroxyquinolate. More preferably, the host is:

In one aspect, the first device is a consumer product. In anotheraspect, the first device is an organic light emitting device.

In one aspect, the device comprises a compound having an emissivespectrum having a peak wavelength of about 650 nm to about 700 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows an exemplary phosphorescent material comprising a quinolineor isoquinoline phenyl ligand further substituted with electron donatinggroups.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, and a cathode 160. Cathode 160 is acompound cathode having a first conductive layer 162 and a secondconductive layer 164. Device 100 may be fabricated by depositing thelayers described, in order. The properties and functions of thesevarious layers, as well as example materials, are described in moredetail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporatedby reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F.sub.4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. patent application Ser. No. 10/233,470, which is incorporated byreference in its entirety. Other suitable deposition methods includespin coating and other solution based processes. Solution basedprocesses are preferably carried out in nitrogen or an inert atmosphere.For the other layers, preferred methods include thermal evaporation.Preferred patterning methods include deposition through a mask, coldwelding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819,which are incorporated by reference in their entireties, and patterningassociated with some of the deposition methods such as ink jet and OVJD.Other methods may also be used. The materials to be deposited may bemodified to make them compatible with a particular deposition method.For example, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, televisions, billboards, lights forinterior or exterior illumination and/or signaling, heads up displays,fully transparent displays, flexible displays, laser printers,telephones, cell phones, personal digital assistants (PDAs), laptopcomputers, digital cameras, camcorders, viewfinders, micro-displays,vehicles, a large area wall, theater or stadium screen, or a sign.Various control mechanisms may be used to control devices fabricated inaccordance with the present invention, including passive matrix andactive matrix. Many of the devices are intended for use in a temperaturerange comfortable to humans, such as 18 degrees C. to 30 degrees C., andmore preferably at room temperature (20-25 degrees C.).

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylkyl,heterocyclic group, aryl, aromatic group, and heteroaryl are known tothe art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32,which are incorporated herein by reference.

Using Ir(3-Meppy)₃ as a base structure, different alkyl substitutionpatterns on both the emitting ligand and the ancillary ligand have beenpreviously studied to establish a structure-property relationship withrespect to material processibility (evaporation temperature, evaporationstability, solubility, etc) and device characteristics ofIr(2-phenylquinoline) and Ir(1-phenylisoquinoline) type phosphorescentmaterials and their PHOLEDs. Alkyl substitutions are particularlyimportant because they offer a wide range of tunability in terms ofevaporation temperature, solubility, energy levels, device efficiencyand narrowness of the emission spectrum. Moreover, they are stablefunctional groups chemically and in device operation when appliedappropriately. Strong electron donating or electron withdrawingsubstituents on the emitting ligand can even further tune the emissionenergy of the complexes. In an effort to create phosphorescent emitterswith very deep red emission, a variety of electron donating groups onthe emitting ligand were studied to determine the extent of the redshifting effect.

The compounds provided herein exhibit very deep red emission in therange of 650 nm to 700 nm. Very deep red emission is useful for certaindisplay applications requiring an emission wavelength between 650 nm and700 nm. In particular, these compounds may be especially useful in OLEDdisplays or other displays requiring very deep red emission.

The compounds disclosed herein comprise a ligand having an quinoline orisoquinoline moiety and a phenyl moiety, e.g., (iso)pq ligands. The(iso)pq ligand provides red emission. The phenyl moiety of the (iso)pqligand is further substituted with electron donating groups, includingalkoxy, aryloxy and amino groups. Without being bound by theory, it isbelieved that substitution of the (iso)pq ligand with electron donatinggroups causes further red shifting and, thus, very deep red emission.

Compounds are provided having the formula:

M is a metal having an atomic weight higher than 40. L is an ancillaryligand. m is the oxidation state of the metal M. Preferably, M is Ir. nis at least 1. A is a fused carbocyclic or fused heterocyclic ring. Byfused, it is meant that A is a carbocyclic or heterocyclic ring that isfused to the pyridine ring of the phenyl pyridine moiety in thecompound. A may be further substituted. Fusing A to the pyridine ringresults in an (iso)pq ligand, as discussed above. Each of R_(a) andR_(b) may represent mono, di, tri, or tetra substituents. Each R_(a)substituent is independently selected from the group consisting ofhydrogen, deuterium, alkyl, heteroalkyl, aryl or heteroaryl groups. EachR_(b) substituent is independently selected from the group consisting ofhydrogen, deuterium, alkyl, heteroalkyl, aryl or heteroaryl groups. Atleast two R_(b) substituents are selected from the group consisting ofalkoxy, aryloxy, alkyl amino, and aryl amino.

Preferably, L is a monoanionic bidentate ligand. More preferably, L is

and R_(x), R_(y), and R_(z) are each independently selected from thegroup consisting of hydrogen, deuterium, alkyl, heteroalkyl, aryl orheteroaryl groups. Most preferably, at least one of R_(x) and R_(y)contains a branched alkyl moiety with branching at a position furtherthan the α position to the carbonyl group. The α position refers to thefirst carbon that attaches to a functional group. In one aspect, atleast one of R_(x) and R_(y) is isobutyl. In another aspect, R_(z) ishydrogen.

In one aspect, the compound has a formula selected from the groupconsisting of:

In another aspect, the (iso)pq ligand is selected from the groupconsisting of:

Specific compounds are also provided. In particular, the compound isselected from the group consisting of:

In one aspect, the compound has an emissive spectrum having a peakwavelength of about 650 nm to about 700 nm.

A first device comprising an organic light emitting device is alsoprovided. The organic light emitting device further comprises an anode,a cathode, and an organic layer disposed between the anode and thecathode. The organic layer comprises a compound having the formula:

M is a metal having an atomic weight higher than 40. Preferably, M isIr. L is an ancillary ligand. m is the oxidation state of the metal M. nis at least 1. A is a fused carbocyclic or fused heterocyclic ring, asdiscussed above. Each of R_(a) and R_(b) may represent mono, di, tri, ortetra substituents. Each R_(a) substituent is independently selectedfrom the group consisting of hydrogen, deuterium, alkyl, heteroalkyl,aryl or heteroaryl groups. Each R_(b) substituent is independentlyselected from the group consisting of hydrogen, deuterium, alkyl,heteroalkyl, aryl or heteroaryl groups. At least two R_(b) substituentsare selected from the group consisting of alkoxy, aryloxy, alkyl amino,and aryl amino.

Preferably, L is a monoanionic bidentate ligand. More preferably, L is

and R_(x), R_(y), and R_(z) are each independently selected from thegroup consisting of hydrogen, deuterium, alkyl, heteroalkyl, aryl orheteroaryl groups. Most preferably, at least one of R_(x) and R_(y)contains a branched alkyl moiety with branching at a position furtherthan the α position to the carbonyl group. In one aspect, at least oneof R_(x) and R_(y) is isobutyl. In another aspect, R_(z) is hydrogen.

In one aspect, the compound has a formula selected from the groupconsisting of:

In another aspect, the (iso)pq ligand is selected from the groupconsisting of:

Specific examples of devices comprising inventive compounds areprovided. In one aspect, the compound is selected from the groupconsisting of Compound 1-Compound 7.

In one aspect, the organic layer is an emissive layer and the compoundhaving Formula I is an emitting dopant. In another aspect, the organiclayer further comprises a host. Preferably, the host is a metal8-hydroxyquinolate. More preferably, the host is:

In one aspect, the first device is a consumer product. In anotheraspect, the first device is an organic light emitting device.

In one aspect, the device comprises a compound having an emissivespectrum having a peak wavelength of about 650 nm to about 700 nm.

In addition, there are several other embodiments; however, theseembodiments are less preferred.

A compound having the formula M(Li)_(m)(L′j)_(n) is provided. M is ametal having an atomic weight higher than 40. m is at least 1. n is atleast 1. m+n is the oxidation state of the metal M. i is an indexingvariable having a value from 1 to m. j is an indexing variable having avalue from 1 to n. Each L independently has the formula:

A and B are each independently a 5 or 6-membered aromatic orheteroaromatic ring. A-B represents a bonded pair of aromatic orheteroaromatic rings coordinated to the metal via a nitrogen atom onring A and an sp² hybridized carbon atom on ring B. Each of R_(a) andR_(b) may represent mono, di, tri, or tetra substituents. Each R_(a)substituent is independently selected from the group consisting ofhydrogen, deuterium, alkyl, heteroalkyl, aryl, or heteroaryl groups.Each R_(b) substituent is independently selected from a group consistingof hydrogen, deuterium, alkyl, heteroalkyl, aryl, or heteroaryl groups,and at least one R_(b) substituent is selected from the group consistingof alkoxy, aryloxy, alkyl amino and arylamino. Each L′ independently hasthe formula:

R_(x), R_(y), R_(z) are each independently selected from the groupconsisting of hydrogen, deuterium, alkyl, heteroalkyl, aryl, orheteroaryl groups. At least one of R_(x) and R_(y) contains a branchedalkyl moiety with branching at a position further than the α position tothe carbonyl group. Preferably, at least one of R_(x) and R_(y) isisobutyl. Preferably, R_(z) is hydrogen.

In one aspect, the compound has the formula:

m is the oxidation state of the metal. M−n is at least 1.

In another aspect, the metal M is Ir.

In yet another aspect, the compound has a formula selected from thegroup consisting of:

In one aspect, the bonded pair of aromatic or heteroaromatic ringsrepresented by A-B is selected from the group consisting of:

Specific non-limiting examples of such compounds include compoundsselected from the group consisting of:

Additionally, a first device comprising an organic light emitting deviceis provided. The organic light emitting device comprises an anode, acathode, and an organic layer, disposed between the anode and thecathode. The organic layer comprises a compound having the formulaM(L_(i))_(m)(L′_(j))_(n). M is a metal having an atomic weight higherthan 40. Preferably, the metal M is Ir. m is at least 1. n is atleast 1. m+n is the oxidation state of the metal M. i is an indexingvariable having a value from 1 to m. j is an indexing variable having avalue from 1 to n. Each L independently has the formula:

A and B are each independently a 5 or 6-membered aromatic orheteroaromatic ring. A-B represents a bonded pair of aromatic orheteroaromatic rings coordinated to the metal via a nitrogen atom onring A and an sp² hybridized carbon atom on ring B. Each of R_(a) andR_(b) may represent mono, di, tri, or tetra substituents. Each R_(a)substituent is independently selected from the group consisting ofhydrogen, deuterium, alkyl, heteroalkyl, aryl, or heteroaryl groups.Each R_(b) substituent is independently selected from a group consistingof hydrogen, deuterium, alkyl, heteroalkyl, aryl, or heteroaryl groups.At least one R_(b) substituent is selected from the group consisting ofalkoxy, aryloxy, alkyl amino and arylamino. Each L′ independently hasthe formula:

R_(x), R_(y), R_(z) are each independently selected from the groupconsisting of hydrogen, deuterium, alkyl, heteroalkyl, aryl, orheteroaryl groups. At least one of R_(x) and R_(y) contains a branchedalkyl moiety with branching at a position further than the α position tothe carbonyl group. Preferably, at least one of R_(x) and R_(y) isisobutyl. Preferably, R_(z) is hydrogen.

The various specific aspects discussed above for compounds having theformula M(L_(i))_(m)(L′_(j))_(n) are also applicable to a compoundhaving the formula M(L_(i))_(m)(L′_(j))_(n) when used in the firstdevice. In particular, specific aspects of M, L_(i), L′_(j), m, n, j, L,A, B, A-B, R_(a), R_(b), R_(x), R_(y), and R_(z) discussed above forcompounds having the formula M(L_(i))_(m)(L′_(j))_(n) are alsoapplicable to a compound having the formula M(L_(i))_(m)(L′_(j))_(n)when used in the first device.

Specific examples of compounds for use in the first device are provided.In one aspect, the compound is selected from the group consisting ofCompound 1-Compound 11.

In one aspect, the organic layer is an emissive layer and the compoundhaving Formula I is an emitting dopant. In another aspect, the organiclayer further comprises a host. Preferably, the host is a metal8-hydroxyquinolate. More preferably, the host is:

In one aspect, the device is a consumer product. In another aspect, thedevice is an organic light emitting device.

Combination with Other Materials

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

HIL/HTL:

A hole injecting/transporting material to be used in embodiments of thepresent invention is not particularly limited, and any compound may beused as long as the compound is typically used as a holeinjecting/transporting material. Examples of the material include, butnot limit to: a phthalocyanine or porphryin derivative; an aromaticamine derivative; an indolocarbazole derivative; a polymer containingfluorohydrocarbon; a polymer with conductivity dopants; a conductingpolymer, such as PEDOT/PSS; a self-assembly monomer derived fromcompounds such as phosphonic acid and sliane derivatives; a metal oxidederivative, such as MoO_(x); a p-type semiconducting organic compound,such as 1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metalcomplex, and a cross-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL include, butnot limit to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting aromatichydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl,triphenylene, naphthalene, anthracene, phenalene, phenanthrene,fluorene, pyrene, chrysene, perylene, azulene; group consisting aromaticheterocyclic compounds such as dibenzothiophene, dibenzofuran,dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene,benzoselenophene, carbazole, indolocarbazole, pyridylindole,pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole,oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine,pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine,indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole,benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline,quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine,phenazine, phenothiazine, phenoxazine, benzofuropyridine,furodipyridine, benzothienopyridine, thienodipyridine,benzoselenophenopyridine, and selenophenodipyridine; and groupconsisting 2 to 10 cyclic structural units which are groups of the sametype or different types selected from the aromatic hydrocarbon cyclicgroup and the aromatic heterocyclic group and are bonded to each otherdirectly or via at least one of oxygen atom, nitrogen atom, sulfur atom,silicon atom, phosphorus atom, boron atom, chain structural unit and thealiphatic cyclic group. Wherein each Ar is further substituted by asubstituent selected from the group consisting of hydrogen, deuterium,alkyl, alkoxy, amino, alkenyl, alkynyl, arylalkyl, heteroalkyl, aryl andheteroaryl.

In one aspect, Ar¹ to Ar⁹ is independently selected from the groupconsisting of:

k is an integer from 1 to 20; X¹ to X⁸ is CH or N; Ar¹ has the samegroup defined above.

Examples of metal complexes used in HIL or HTL include, but not limit tothe following general formula:

M is a metal, having an atomic weight greater than 40; (Y¹—Y²) is abidentate ligand, Y1 and Y² are independently selected from C, N, O, P,and S; L is an ancillary ligand; m is an integer value from 1 to themaximum number of ligands that may be attached to the metal; and m+n isthe maximum number of ligands that may be attached to the metal.

In one aspect, (Y¹—Y²) is a 2-phenylpyridine derivative.

In another aspect, (Y¹—Y²) is a carbene ligand.

In another aspect, M is selected from Ir, Pt, Os, and Zn.

In a further aspect, the metal complex has a smallest oxidationpotential in solution vs. Fc⁺/Fc couple less than about 0.6 V.

Host:

The light emitting layer of the organic EL device in embodiments of thepresent invention preferably contains at least a metal complex as lightemitting material, and may contain a host material using the metalcomplex as a dopant material. Examples of the host material are notparticularly limited, and any metal complexes or organic compounds maybe used as long as the triplet energy of the host is larger than that ofthe dopant.

Examples of metal complexes used as host are preferred to have thefollowing general formula:

M is a metal; (Y³—Y⁴) is a bidentate ligand, Y³ and Y⁴ are independentlyselected from C, N, O, P, and S; L is an ancillary ligand; m is aninteger value from 1 to the maximum number of ligands that may beattached to the metal; and m+n is the maximum number of ligands that maybe attached to the metal.

In one aspect, the metal complexes are:

(O—N) is a bidentate ligand, having metal coordinated to atoms O and N.

In another aspect, M is selected from Ir and Pt.

In a further aspect, (Y³—Y⁴) is a carbene ligand.

Examples of organic compounds used as host are selected from the groupconsisting aromatic hydrocarbon cyclic compounds such as benzene,biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene,phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; groupconsisting aromatic heterocyclic compounds such as dibenzothiophene,dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran,benzothiophene, benzoselenophene, carbazole, indolocarbazole,pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole,oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole,pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine,oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine,benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline,cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine,pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine,benzofuropyridine, furodipyridine, benzothienopyridine,thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine;and group consisting 2 to 10 cyclic structural units which are groups ofthe same type or different types selected from the aromatic hydrocarboncyclic group and the aromatic heterocyclic group and are bonded to eachother directly or via at least one of oxygen atom, nitrogen atom, sulfuratom, silicon atom, phosphorus atom, boron atom, chain structural unitand the aliphatic cyclic group. Wherein each group is furthersubstituted by a substituent selected from the group consisting ofhydrogen, deuterium, alkyl, alkoxy, amino, alkenyl, alkynyl, arylalkyl,heteroalkyl, aryl and heteroaryl.

In one aspect, the host compound contains at least one of the followinggroups in the molecule:

R¹ to R⁷ are independently selected from the group consisting ofhydrogen, deuterium, alkyl, alkoxy, amino, alkenyl, alkynyl, arylalkyl,heteroalkyl, aryl and heteroaryl, when it is aryl or heteroaryl, it hasthe similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from CH or N.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holesand/or excitons that leave the emissive layer. The presence of such ablocking layer in a device may result in substantially higherefficiencies as compared to a similar device lacking a blocking layer.Also, a blocking layer may be used to confine emission to a desiredregion of an OLED.

In one aspect, compound used in HBL contains the same molecule used ashost described above.

In another aspect, compound used in HBL contains at least one of thefollowing groups in the molecule:

k is an integer from 0 to 20; L is an ancillary ligand, m is an integerfrom 1 to 3.

ETL:

Electron transport layer (ETL) may include a material capable oftransporting electrons. Electron transport layer may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity.Examples of the ETL material are not particularly limited, and any metalcomplexes or organic compounds may be used as long as they are typicallyused to transport electrons.

In one aspect, compound used in ETL contains at least one of thefollowing groups in the molecule:

R¹ is selected from the group consisting of hydrogen, deuterium, alkyl,alkoxy, amino, alkenyl, alkynyl, arylalkyl, heteroalkyl, aryl andheteroaryl, when it is aryl or heteroaryl, it has the similar definitionas Ar's mentioned above.

Ar¹ to Ar³ has the similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from CH or N.

In another aspect, the metal complexes used in ETL contains, but notlimit to the following general formula:

(O—N) or (N—N) is a bidentate ligand, having metal coordinated to atomsO, N or N, N; L is an ancillary ligand; m is an integer value from 1 tothe maximum number of ligands that may be attached to the metal.

In any above-mentioned compounds used in each layer of OLED device, thehydrogen atoms can be partially or fully deuterated.

In addition to and/or in combination with the materials disclosedherein, many hole injection materials, hole transporting materials, hostmaterials, dopant materials, exiton/hole blocking layer materials,electron transporting and electron injecting materials may be used in anOLED. Non-limiting examples of the materials that may be used in an OLEDin combination with materials disclosed herein are listed in Table 1below. Table 1 lists non-limiting classes of materials, non-limitingexamples of compounds for each class, and references that disclose thematerials.

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EXPERIMENTAL Compound Examples

Several of the compounds were synthesized as follows:

Example 1 Synthesis of Compound 1

Step 1. 2-chloroquinoline (9.0 g, 54.4 mmol), 3,5-dimethoxyphenylboronicacid (9.2 g, 59.8 mmol), Pd(PPh₃)₄ (1.8 g, 1.5 mmol), K₂CO₃ (22.4 g, 163mmol), 1,2-dimethoxyethane (150 mL) and water (150 mL) were charged in a500 mL round bottom flask. The reaction mixture was heated to refluxunder nitrogen for 18 h. The reaction mixture was then cooled to ambientand the organic phase was separated from the aqueous phase. The aqueousphase was washed with ethyl acetate and all the organic components werecombined and dried over anhydrous magnesium sulphate. The solvent wasthen removed under vacuum and the product was purified using silica gelchromatography (10% ethyl acetate in hexane as eluent). The materialobtained was further purified by vacuum distillation to yield 12.2 g(95% yield) of product as a colorless oil.

Step 2. The ligand from Step 1 (16.54 g, 71 mmol), 2-ethoxyethanol (250mL) and water (50 mL) were charged in a 1 L three-neck round bottomflask. Nitrogen gas was bubbled through the reaction mixture for 45minutes. IrCl₃.3H₂O (5.0 g, 15 mmol) was then added and the reactionmixture was heated to reflux under nitrogen for 17 h. The reactionmixture was cooled to ambient temperature. Approximately half of thesolvent was removed on the rotary evaporator and 200 mL of ethoxyethanolwas added to the reaction mixture. The iridium dimer was not isolatedand the reaction mixture was used as is for the following step.

Step 3. 2,8-dimethylnonane-4,6-dione (28 g, 152 mmol) and Na₂CO₃ (16 g,152 mmol) were added to the dichlorobridged Iridium dimer solution fromStep 2. The reaction mixture was stirred at room temperature for 48 h.The solvent was removed on the rotary evaporator and the crude dissolvedin dichloromethane. The solution was passed through a 1 inch thicksilica gel plug to remove and salts. The solution was removed and thecrude was purified using silica gel chromatography with dichloromethaneand hexanes as the mobile phase to give 8.0 g of product (73.5% yield).

Example 2 Synthesis of Compound 2

Step 1. 2-chloroquinoline (10.0 g, 61.3 mmol), 3-methoxyphenylboronicacid (9.2 g, 67.5 mmol), Pd(PPh₃)₄ (1.8 g, 1.5 mmol), K₂CO₃ (22.4 g, 163mmol), 1,2-dimethoxyethane (150 mL) and water (150 mL) were charged in a500 mL round bottom flask. The reaction mixture was heated to refluxunder nitrogen for 18 h. The reaction mixture was then cooled to ambienttemperature and the organic phase was separated from the aqueous phase.The aqueous phase was washed with ethyl acetate and all the organiccomponents were combined and dried over anhydrous magnesium sulfate. Thesolvent was then removed under vacuum and the product was purified usingsilica gel chromatography (10% ethyl acetate in hexane as eluent). Thematerial obtained was further purified by vacuum distillation to yield13.0 g (90% yield) of product as a colorless oil.

Step 2. The ligand from Step 1 (10.0 g, 42.5 mmol), 2-ethoxyethanol (200mL) and water (40 mL) were charged in a 1 L three-neck round bottomflask. Nitrogen gas was bubbled through the reaction mixture for 45minutes. IrCl₃.3H₂O (4.0 g, 10.6 mmol) was then added and the reactionmixture was heated to reflux under nitrogen for 17 h. The reactionmixture was cooled to ambient temperature. Approximately half of thesolvent was removed on the rotary evaporator and 200 mL of ethoxyethanolwas added to the reaction mixture. The iridium dimer was not isolatedand the reaction mixture was used as is for the following step.

Step 3. 2,8-dimethylnonane-4,6-dione (20 g, 108 mmol) and Na₂CO₃ (11.23g, 106 mmol) were added to the dichlorobridged Iridium dimer solutionfrom Step 2. The reaction mixture was stirred at room temperature for 48h. The solvent was removed on the rotary evaporator and the crudedissolved in dichloromethane. The solution was passed through a 1 inchthick silica gel plug to remove and salts. The solution was removed andthe crude was purified using silica gel chromatography withdichloromethane and hexanes as the mobile phase to give 5.0 g of product(52% yield).

Device Examples

All device examples were fabricated by high vacuum (<10⁻⁷ Torr) thermalevaporation. The anode electrode is 1200 Å of indium tin oxide (ITO).The cathode consisted of 10 Å of LiF followed by 1000 Å of Al. Alldevices were encapsulated with a glass lid sealed with an epoxy resin ina nitrogen glove box (<1 ppm of H₂O and O₂) immediately afterfabrication, and a moisture getter was incorporated inside the package.

The organic stack of the Device Example consisted of sequentially, fromthe ITO surface, 100 Å of hole injection layer (HIL), 300 Å of4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD) as the holetransporting later (HTL), 300 Å of host (CBP or Compound D) doped with9% of Compound 1-2 as the emissive layer (EML), and 400 Å of Alq₃(tris-8-hydroxyquinoline aluminum) as the ETL.

As used herein, the following compounds have the following structures:

Particular emissive dopants for the emissive layer of an OLED areprovided. These compounds may lead to devices having particularly goodproperties. The device structures are provided in Table 2, and thecorresponding device data is provided in Table 3.

TABLE 2 VTE PHOLEDs Device Example HIL HTL EML(doping %) ETL Example 1Compound C α-NPD Compound D Compound 1 Alq₃ (9%) Example 2 Compound Cα-NPD Compound D Compound 2 Alq₃ (9%) Comparative Compound C α-NPD CBPCompound A Alq₃ Example 1 (9%) Comparative Compound C α-NPD Compound DCompound B Alq₃ Example 2 (9%)

TABLE 3 VTE Device data CIE At 1000 cd/m2 at J = 40 mA/cm2 Device λmaxFWHM CIE CIE V LE EQE PE LE/ L₀, RT_(80%) Example (nm) (nm) (x) (y) [V](cd/A) (%) (lm/W) EQE (cd/m²) (h) Example 1 672 81 0.71 0.29 15 1.1 5.80.2 0.2 546 60 Example 2 685 98 0.71 0.28 16.8 0.5 4.1 0.1 0.1 321 200Comparative 622 62 0.67 0.33 8.1 19.9 18.9 7.7 1.1 6447 888 Example 1Comparative 636 64 0.70 0.30 9.9 10.5 18.5 3.3 0.6 3408 799 Example 2

In particular, Device Examples 1 and 2 are significantly red shifted(>40 nm) from Comparative Example 1 and Comparative Example 2. Thissuggests that having 2 strong electron donating alkoxy groups comparedto alkyl groups causes a marked reduction in the HOMO-LUMO gap,resulting in low energy emission in the deep red part of the visiblespectrum.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore includes variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

1. A compound having a formula:

wherein M is a metal having an atomic weight higher than 40; wherein Lis an ancillary ligand; wherein m is the oxidation state of the metal M;wherein n is at least 1; wherein A is a fused carbocyclic or fusedheterocyclic ring; wherein each of R_(a) and R_(b) may represent mono,di, tri, or tetra substituents; wherein each R_(a) substituent isindependently selected from the group consisting of hydrogen, deuterium,alkyl, heteroalkyl, aryl or heteroaryl groups; wherein each R_(b)substituent is independently selected from the group consisting ofhydrogen, deuterium, alkyl, heteroalkyl, aryl or heteroaryl groups; andwherein at least two R_(b) substituents are selected from the groupconsisting of alkoxy, aryloxy, alkyl amino, and aryl amino.
 2. Thecompound of claim 1, wherein M is Ir.
 3. The compound of claim 1,wherein L is a monoanionic bidentate ligand.
 4. The compound of claim 1,wherein L is

and wherein R_(x), R_(y), and R_(z), are each independently selectedfrom the group consisting of hydrogen, deuterium, alkyl, heteroalkyl,aryl or heteroaryl groups.
 5. The compound of claim 1, wherein thecompound has a formula selected from the group consisting of:


6. The compound of claim 5, wherein at least one of R_(x) and R_(y)contains a branched alkyl moiety with branching at a position furtherthan the α position to the carbonyl group.
 7. The compound of claim 5,wherein at least one of R_(x) and R_(y) is isobutyl.
 8. The compound ofclaim 5, wherein R_(z) is hydrogen.
 9. The compound of claim 1, whereinthe (iso)pq ligand is selected from the group consisting of:


10. The compound of claim 1, wherein the compound is selected from thegroup consisting of:


11. The compound of claim 1, wherein the compound has an emissivespectrum having a peak wavelength of about 650 nm to about 700 nm.
 12. Afirst device, comprising an organic light emitting device furthercomprising: an anode; a cathode; and an organic layer, disposed betweenthe anode and the cathode, comprising a compound having a formula:

wherein M is a metal having an atomic weight higher than 40; wherein Lis an ancillary ligand; wherein m is the oxidation state of the metal M;wherein n is at least 1; wherein A is a fused carbocyclic or fusedheterocyclic ring; wherein each of R_(a) and R_(b) may represent mono,di, tri, or tetra substituents; wherein each R_(a) substituent isindependently selected from the group consisting of hydrogen, deuterium,alkyl, heteroalkyl, aryl or heteroaryl groups; wherein each R_(b)substituent is independently selected from the group consisting ofhydrogen, deuterium, alkyl, heteroalkyl, aryl or heteroaryl groups; andwherein at least two R_(b) substituents are selected from the groupconsisting of alkoxy, aryloxy, alkyl amino, and aryl amino.
 13. Thefirst device of claim 12, wherein M is Ir.
 14. The first device of claim12, wherein L is a monoanionic bidentate ligand.
 15. The first device ofclaim 12, wherein L is

and wherein R_(x), R_(y), and R_(z) are each independently selected fromthe group consisting of hydrogen, deuterium, alkyl, heteroalkyl, aryl orheteroaryl groups.
 16. The first device of claim 12, wherein thecompound has a formula selected from the group consisting of:


17. The first device of claim 16, wherein at least one of R_(x) andR_(y) contains a branched alkyl moiety with branching at a positionfurther than the α position to the carbonyl group.
 18. The first deviceof claim 16, wherein at least one of R_(x) and R_(y) is isobutyl. 19.The first device of claim 16, wherein R_(z) is hydrogen.
 20. The firstdevice of claim 12, wherein the (iso)pq ligand is selected from thegroup consisting of:


21. The first device of claim 12, wherein the compound is selected fromthe group consisting of:


22. The first device of claim 12, wherein the organic layer is anemissive layer and the compound having Formula I is an emitting dopant.23. The first device of claim 22, wherein the organic layer furthercomprises a host.
 24. The first device of claim 23, wherein the hose isa metal 8-hydroxyquinolate.
 25. The first device of claim 23, whereinthe host is:


26. The first device of claim 12, wherein the first device is a consumerproduct.
 27. The first device of claim 12, wherein the first device isan organic light emitting device.
 28. The first device of claim 12,wherein the compound has an emissive spectrum having a peak wavelengthof about 650 nm to about 700 nm.